1. Fields of the Invention
This invention relates to a radiant furnace capable of efficiently achieving very high and uniform temperatures in a very clean environment.
2. Description of Related Art
A variety of radiant furnace designs are known for the purpose of producing high temperature environments in which semiconductors and other materials can be processed. Unfortunately, the structure of those prior art designs often severely limits their maximum temperature capabilities and/or their ability to produce uniform heating, as well as their energy efficiency. Such prior art furnaces also tend to be expensive to build and operate.
U.S. Pat. No. 3,862,397 is typical of many cool walled radiantly heated reactors. The workpiece is surrounded by a bell jar which is heated from the outside by a plurality of lamps. Reflectors are placed behind each of the lamps in order to concentrate energy, and a suitable coolant, such as air, passes through the hollow reflectors and between the radiant elements and the bell jar in order to keep the environment relatively cool.
Similarly, U.S. Pat. No. 3,316,387 discloses an electric lamp employing a heated sheet radiator. A Reflective surface is also employed as well as cooling fluid between two sheets of quartz.
U.S. Pat. No. 4,375,027 discloses a dual chambered high pressure furnace which employs blanket gases in the cooling chamber. A quartz crucible surrounds the heated area.
U.S. Pat. No. 4,101,759 discusses the use of cooling gases in the context of a semiconductor body heater in which the radiant heat is provided by a plurality of tungsten filament quartz lamps behind which a reflective surface is located.
U.S. Pat. No. 4,511,788 describes a light-radiant heating furnace which is cooled by water rather than gas.
U.S. Pat. Nos. 4,081,313 and 4,097,226 describe other furnace structures of lesser relevance.
The foreign patent literature also describes efforts to produce high efficiency, low cost radiant furnace devices.
For example, Japanese Patent No. 56-48128A discloses a heat treatment invention in which semiconductor substrates are directly heated by radiation from infrared lamps. Gas is introduced between a quartz reactor tube and the infrared lamps to cool the reactor. Surface reflectors are provided behind the lamps to improve the heating of the substrate. Japanese Patent No. 52532A/29 describes an electric oven including interconnected heating segments and a reflective wall assembly to correct for lack of uniformity of heating.
British Patent No. 1,466,99 describes a laboratory furnace having a refractory lining insulation which includes reflective surfaces for reflecting heat towards the center of the apparatus.
Lastly, British Patent No. 1,036,905 discloses a furnace in which gases are passed between an inner and outer tube, though it is not clear if the purpose of the gases is to provide cooling.
While the foregoing patents are typical of the prior art, they are not believed to have been able to achieve the high uniform temperatures, heating rates, economy, and efficiency of the present invention.